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lit is a portable tool for executing LLVM and Clang style test
suites, summarizing their results, and providing indication of failures.
lit is designed to be a lightweight testing tool with as simple a
user interface as possible.

lit should be run with one or more tests to run specified on the
command line. Tests can be either individual test files or directories to
search for tests (see TEST DISCOVERY).

Each specified test will be executed (potentially in parallel) and once all
tests have been run lit will print summary information on the number
of tests which passed or failed (see TEST STATUS RESULTS). The
lit program will execute with a non-zero exit code if any tests
fail.

By default lit will use a succinct progress display and will only
print summary information for test failures. See OUTPUT OPTIONS for
options controlling the lit progress display and output.

lit also includes a number of options for controlling how tests are
executed (specific features may depend on the particular test format). See
EXECUTION OPTIONS for more information.

Finally, lit also supports additional options for only running a
subset of the options specified on the command line, see
SELECTION OPTIONS for more information.

Users interested in the lit architecture or designing a
lit testing implementation should see LIT INFRASTRUCTURE.

When --vg is used, enable memory leak checks. When this option is
enabled, lit will also automatically provide a “vg_leak”
feature that can be used to conditionally disable (or expect failure in)
certain tests.

Track the wall time individual tests take to execute and includes the results
in the summary output. This is useful for determining which tests in a test
suite take the most time to execute. Note that this option is most useful
with -j1.

lit will exit with an exit code of 1 if there are any FAIL or XPASS
results. Otherwise, it will exit with the status 0. Other exit codes are used
for non-test related failures (for example a user error or an internal program
error).

The inputs passed to lit can be either individual tests, or entire
directories or hierarchies of tests to run. When lit starts up, the
first thing it does is convert the inputs into a complete list of tests to run
as part of test discovery.

In the lit model, every test must exist inside some test suite.
lit resolves the inputs specified on the command line to test suites
by searching upwards from the input path until it finds a lit.cfg or
lit.site.cfg file. These files serve as both a marker of test suites
and as configuration files which lit loads in order to understand
how to find and run the tests inside the test suite.

Once lit has mapped the inputs into test suites it traverses the
list of inputs adding tests for individual files and recursively searching for
tests in directories.

This behavior makes it easy to specify a subset of tests to run, while still
allowing the test suite configuration to control exactly how tests are
interpreted. In addition, lit always identifies tests by the test
suite they are in, and their relative path inside the test suite. For
appropriately configured projects, this allows lit to provide
convenient and flexible support for out-of-tree builds.

The test failed, but that is expected. This is used for test formats which allow
specifying that a test does not currently work, but wish to leave it in the test
suite.

XPASS

The test succeeded, but it was expected to fail. This is used for tests which
were specified as expected to fail, but are now succeeding (generally because
the feature they test was broken and has been fixed).

FAIL

The test failed.

UNRESOLVED

The test result could not be determined. For example, this occurs when the test
could not be run, the test itself is invalid, or the test was interrupted.

UNSUPPORTED

The test is not supported in this environment. This is used by test formats
which can report unsupported tests.

Depending on the test format tests may produce additional information about
their status (generally only for failures). See the OUTPUT OPTIONS
section for more information.

This section describes the lit testing architecture for users interested in
creating a new lit testing implementation, or extending an existing one.

lit proper is primarily an infrastructure for discovering and running
arbitrary tests, and to expose a single convenient interface to these
tests. lit itself doesn’t know how to run tests, rather this logic is
defined by test suites.

As described in TEST DISCOVERY, tests are always located inside a test
suite. Test suites serve to define the format of the tests they contain, the
logic for finding those tests, and any additional information to run the tests.

lit identifies test suites as directories containing lit.cfg or
lit.site.cfg files (see also --config-prefix). Test suites are
initially discovered by recursively searching up the directory hierarchy for
all the input files passed on the command line. You can use
--show-suites to display the discovered test suites at startup.

Once a test suite is discovered, its config file is loaded. Config files
themselves are Python modules which will be executed. When the config file is
executed, two important global variables are predefined:

This is the config object (a TestingConfig instance) for the test suite,
which the config file is expected to populate. The following variables are also
available on the config object, some of which must be set by the config and
others are optional or predefined:

name[required] The name of the test suite, for use in reports and
diagnostics.

test_format[required] The test format object which will be used to
discover and run tests in the test suite. Generally this will be a builtin test
format available from the lit.formats module.

test_source_root The filesystem path to the test suite root. For out-of-dir
builds this is the directory that will be scanned for tests.

test_exec_root For out-of-dir builds, the path to the test suite root inside
the object directory. This is where tests will be run and temporary output files
placed.

environment A dictionary representing the environment to use when executing
tests in the suite.

suffixes For lit test formats which scan directories for tests, this
variable is a list of suffixes to identify test files. Used by: ShTest.

substitutions For lit test formats which substitute variables into a test
script, the list of substitutions to perform. Used by: ShTest.

unsupported Mark an unsupported directory, all tests within it will be
reported as unsupported. Used by: ShTest.

parent The parent configuration, this is the config object for the directory
containing the test suite, or None.

root The root configuration. This is the top-most lit configuration in
the project.

pipefail Normally a test using a shell pipe fails if any of the commands
on the pipe fail. If this is not desired, setting this variable to false
makes the test fail only if the last command in the pipe fails.

Once test suites are located, lit recursively traverses the source
directory (following test_source_root) looking for tests. When lit
enters a sub-directory, it first checks to see if a nested test suite is
defined in that directory. If so, it loads that test suite recursively,
otherwise it instantiates a local test config for the directory (see
LOCAL CONFIGURATION FILES).

Tests are identified by the test suite they are contained within, and the
relative path inside that suite. Note that the relative path may not refer to
an actual file on disk; some test formats (such as GoogleTest) define
“virtual tests” which have a path that contains both the path to the actual
test file and a subpath to identify the virtual test.

When lit loads a subdirectory in a test suite, it instantiates a
local test configuration by cloning the configuration for the parent directory
— the root of this configuration chain will always be a test suite. Once the
test configuration is cloned lit checks for a lit.local.cfg file
in the subdirectory. If present, this file will be loaded and can be used to
specialize the configuration for each individual directory. This facility can
be used to define subdirectories of optional tests, or to change other
configuration parameters — for example, to change the test format, or the
suffixes which identify test files.

The lit output for a test run conforms to the following schema, in
both short and verbose modes (although in short mode no PASS lines will be
shown). This schema has been chosen to be relatively easy to reliably parse by
a machine (for example in buildbot log scraping), and for other tools to
generate.

Each test result is expected to appear on a line that matches:

<result code>: <test name> (<progress info>)

where <result-code> is a standard test result such as PASS, FAIL, XFAIL,
XPASS, UNRESOLVED, or UNSUPPORTED. The performance result codes of IMPROVED and
REGRESSED are also allowed.

The <testname> field can consist of an arbitrary string containing no
newline.

The <progressinfo> field can be used to report progress information such
as (1/300) or can be empty, but even when empty the parentheses are required.

Each test result may include additional (multiline) log information in the
following format:

where <testname> should be the name of a preceding reported test, <logdelineator> is a string of “*” characters at least four characters long
(the recommended length is 20), and <trailingdelineator> is an arbitrary
(unparsed) string.

The following is an example of a test run output which consists of four tests A,
B, C, and D, and a log message for the failing test C: